AK2574 Datasheet, PDF (14/30 Pages) Asahi Kasei Microsystems – 156M Laser Diode Driver + APC for Burst Mode

ASAHI KASEI
[AK2574]
2. LD Driver
Fig 2-1 illustrates the block diagram of LD driver function.
The AK2574 LD driver contains a Driver part, an APC part, a LVPECL I/F part and a programmable duty
adjustment.
The driver part is composed of 156M MOD current switching controlled by DATA, and BIAS current switching
controlled by BRST.
APC part is composed of a programmable BIAS and MOD currents in response to the temperature (APC_FF), an
on-chip temperature sensor, and 2 current DACS (I-DAC1 and I-DAC2).
The LVPECL I/F part is composed of LVPECL I/F for data, clock and the burst controlsignal (BRST).
Fig 2-1 Driver Block Diagram
DATAP
DATAN
CLKP
CLKN
BRSTP
BRSTN
DATA ^data
(LVPECL)
SEL
data_ff
FF
AND
DUTY_
ADJ
IMODN
LD
IMOD
CLK
(LVPECL)
clk
SEL
CLKALM
BRST brst
(LVPECL)
FF
LVPECL I/F
brst_ff
Driver
APC
vtemp
TEMP_SENS
ADC
R_DAC1
R_TEMP _EEPEOM
R_DAC2
I-DAC1
I-DAC2
Imod
Ibias
IBIAS
IBIASR1
IBIASC1
330Ω
0.1uF
IBIASC2
0.1uF
2.1 Driver
The 156M MOD driver is composed of the differential current switches, and it sinks the MOD current from IMOD pin
when DATA (DATAP – DATAN) = 1 and sinks the current from IMODN when DATA = 0. DATA is set “0” when
BRST (BRSTP – BRSTN) = 0.
The BIAS driver is composed of the single-end current switch, and it sinks the BIAS current from IBIAS when
BRTS=1. To protect the last LD current at BRST 1→0, BIAS current turned off timing is delayed for a duty extended
when the last DATA=1.
2.2 LVPECL I/F (DATAP, DATAN, CLKP, CLKN, BRSTP, BRTSN)
The AK2574 supports direct data or latched data input (see Table 2-1). Connect CLKP = VDD or leave open and
CLKN = VSS when SEL = “L”.
Table 2-1 Data input
SEL (CMOS)
“L”
“H”
Direct data
Latched data with clock
2.2.1 LVPECL Input Characteristics
Table 2-2 shows LVPECL input characteristics. The AK2574 LVPECL input, which is biased to 0.6 * VDD with 10k
Ω or more impedance respectively.
<MS0266-E-00>
-14-
2003/12